[Show abstract][Hide abstract] ABSTRACT: To gain a better understanding of the direct actions of halothane on myocardial function in ischaemia, we studied the effects of increasing extracellular potassium concentration and decreasing extracellular pH (acidosis), alone or in combination with halothane, on the contractile force and resting tension in isolated atria. Guinea pig left atria were superfused with Tyrode's solution and stimulated at 1 Hz. Isometric contractile force and resting tension were measured using a force displacement transducer. Perfusate potassium concentrations were increased from 5.4 mmol.L-1 to either 8.1 mmol.L-1 or 10.8 mmol.L-1 by adding KCl to the standard Tyrode's solution, and its pH was decreased from 7.4 to either 7.0 or 6.5 by decreasing bicarbonate. In standard Tyrode's solution (potassium 5.4 mmol.L-1, pH 7.4), halothane 0.5-2% reduced contractile force in a dose-dependent manner (P < 0.05); the effective concentration of halothane for 50% inhibition of contractile force (IC50) was 1.3%. Both increasing extracellular potassium and decreasing extracellular pH decreased the contractile force in a potassium- or pH-dependent fashion. The negative inotropism of halothane (1%) was not altered by increasing potassium concentrations, whereas 1% halothane caused a greater decrease in contractile force at pH 6.5 than at pH 7.4. Halothane (1%) enhanced the acidosis (pH 6.5)-induced increases in resting tension. Arrhythmias were produced in one of eight preparations during acidosis, while four of eight preparations demonstrated arrhythmias during acidosis in the presence of halothane. These data suggest that acidosis and halothane may have a synergistic interaction on the contractile force and resting tension of the atria.(ABSTRACT TRUNCATED AT 250 WORDS)
Canadian Journal of Anaesthesia 07/1994; 41(6):534-41. · 2.50 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We studied in patients the effect of d-tubocurarine, which has sympathetic ganglion blocking action, on succinylcholine-induced increases in plasma levels of catecholamines, and compared it with the effects of vecuronium and pancuronium, which have little sympathetic ganglion blocking action. Thirty-two patients were divided into five groups: seven were given 3 mL saline; seven received 1 mg/kg succinylcholine; and six, seven, and five patients were given 0.08 mg/kg d-tubocurarine, 0.01 mg/kg vecuronium, and 0.01 mg/kg pancuronium, respectively, all of which were injected 5 min before 1 mg/kg succinylcholine. Succinylcholine alone significantly increased plasma norepinephrine concentrations, systolic blood pressure, and heart rate from 187 +/- 39 pg/mL (mean +/- SEM), 93 +/- 2 mm Hg, and 77 +/- 4 beats/min to 429 +/- 61 pg/mL, 120 +/- 7 mm Hg, and 102 +/- 6 beats/min, respectively, with onset of fasciculations. Pretreatment with d-tubocurarine, vecuronium, and pancuronium significantly and equally attenuated both the fasciculations and the cardiovascular responses to succinylcholine. These results suggest that the sympathetic ganglion blocking action of neuromuscular relaxants when given before succinylcholine is not an important factor in attenuation of succinylcholine-induced increases in plasma levels of catecholamines.